In the field of stage and studio lighting for instance, or in any projection lighting application such as flood or spot lighting systems, it is necessary to deliver a high brightness light output to a particular area at a distance from the projection system. In such an application, there must be sufficient light output to insure that the object or person on the stage for instance is clearly displayed. To date, such a projection lighting system has typically utilized a light source such as a high intensity discharge light source of approximately 200 Watts or greater for small, portable projection devices. In addition to requiring a high amount of energy to power such a light source, the typical lamp utilized for this purpose would have a rated life of approximately 250 hours. An example of such a projection lighting device can be found for example in a product offering by the Mole-Richardson Company as their Spot-to-Flood Projection Lighting Device, Model No. 6191. In such a device, the light source is provided by OSRAM Lighting Company by their 200 Watt, HMI Metallogen (R) Lamp, which as previously discussed, is limited in terms of energy efficiency and rated life. Additionally, such a high wattage light source generates a significant amount of heat as compared to a lower wattage device of perhaps 50 to 75 watts. It would therefore be advantageous to the field of projection lighting if a light source could be provided that utilized a more energy efficient light source which not only exhibited significantly greater temperature performance characteristics relative to the higher wattage lamps, but also provided a significant extension in the rated life of such lamp, such as for instance, a rated life in excess of 5000 hours which is 20 times that of the light source presently in use.
Another problem with the prior art projection lighting system such as defined above relates to the need to mask off certain portions of the projected light image so as to eliminate the appearance of any color separation in the light output. In other words, the presently known systems exhibit a deficiency in the area of spatial separation of the light output. The image of the light output of known light sources will exhibit a center, high intensity region that is white in color with a outer, less intense region which is red in color. As such, since it is desired to project only the high intensity, white center region to the area of illumination, a masking device is typically used to block the red, outer region of the light output. Such a masking operation has been found to be inefficient because of the elimination of what may otherwise be usable light output (the outer region) and in addition, because the light output of a typical high intensity discharge lamp used in projection lighting devices is subject to wandering of the arc discharge within the arc chamber, the white center region can be displaced by the red outer region with such red outer region then being projected through the mask. Accordingly, it would be desirable if a light source and light delivery arrangement could be provided that would utilize as much of the light output from the source as possible without experiencing the problem of spatial variation or the appearance of a color variation at the point of illumination.
One approach to substantially reducing the effects of color variation in the image of the light output from a high intensity light source can be found in U.S. Pat. application Ser. No. 07/859,179, filed on Mar. 27, 1992 by Davenport et al. and assigned to the same assignee as the present invention. In this application, a polygonal shaped optical coupling device is disclosed having the properties of uniform light output in terms of color and intensity. In utilizing such an optical coupling device for a projection lighting system as used in the stage and studio field however, it is necessary to consider the size constraints to a system that is intended to be hand-held and portable. Therefore, any design of an improved projection lighting device having a uniform color output should provide a physical configuration that does not increase the dimensions of housing components presently used for existing projection systems. Such a physical size consideration may require the use of light turning elements that could manipulate the light output so as to be coupled in as compact a space as possible. It should also be noted however, that in such light turning applications, there is a possibility that the coupling efficiency could be sacrificed given that for every bounce of light output that occurs, a measurable light loss is associated therewith. Accordingly, it would be further advantageous if a light re-directing arrangement could be included that not only allowed for the use of an improved light source, delivery arrangement in an existing size housing, but did not result in a considerable loss of light output in performing such light re-directing.